1. Field of the Invention
The present invention relates to a yoke for a universal joint adapted for use for example in the steering device of an automobile for transmitting the movement of the steering column to the steering gear, and a manufacturing method therefor.
2. Related Background Art
The steering device of an automobile is constructed, for example, as shown in FIG. 5.
The movement of a steering wheel 1 is transmitted through a steering shaft 2 and a connecting rod 3 to steering gears 4 which steer the wheels of the automobile.
Because, the steering shaft 2 and the input shaft 5 of the steering gears 4 cannot, in general, be mutually aligned, the connecting rod 3 is usually provided between two shafts 2, 5 and the ends of said connecting rod 3 are connected to the ends of said shafts 2, 5 through universal joints 6, 6 whereby the movement transmission is enabled between the mutually unaligned shafts 2 and 5.
The universal joint 6 incorporated in such power transmission mechanism is conventionally composed, as shown in FIG. 6, of first and second yokes 7, 8 of bifurcate form, and a cross-shaped shaft 9 for movably combining said yokes 7, 8.
In the universal joint shown in FIG. 6, since each yoke is prepared by pressing a metal plate as disclosed in the Japanese Patent Application No. 63-185222, the positional relationship between the coupling arms for supporting the cross-shaped shaft 9 and the flange (to be tightened with a bolt for connecting the yoke for example to the end of the connecting rod 3 is not adjustable but is always fixed. Consequently, the fixation of the bolt on the flange becomes sometimes difficult in certain conditions of use.
For avoiding such drawback, there is already known a structure, as shown in FIGS. 7 and 8, composed of a combination of a coupling tube 10, coupling arms 11 and a clamping member 12.
The coupling tube 10 is formed by drawing a metal pipe, and is provided with a slit 13 in a radial direction and serrate grooves 14 on the internal periphery, both formed by suitable mechanical working.
The coupling arms 11 are formed by pressing a metal plate in U-shaped form, which is provided with a hole 15 at the base portion, and mutually coaxial circular holes 16, 16 at both ends.
The clamp member 12 is formed by forging and then mechanically working a metal material, and is provided with a screw hole 17 at an end and a hole 18 at the other end for passing a bolt (not shown) to be screwed into said screw hole 17.
The above-mentioned members 10, 11, 12 are combined by fitting the clamp member 12 on an end of the coupling tube, fitting the hole 15 at the base portion of the coupling arms 11 on the other end of the coupling tube 10, and welding the fitted portions, thereby completing a yoke 7 (or 8) for the universal joint.
When such yoke 7 (or 8) is connected to the end for example of the connecting rod 3 (FIG. 5), a serrate portion formed on said end portion of the connecting rod is inserted into the coupling tube 10 while the bolt fitted into said clamp is loosened, and said bolt is then tightened. Thus the yoke 7 (or 8) is firmly coupled to the end of the connecting rod 3.
However, the above-explained yoke of the conventional universal joint has the drawbacks of requiring many (three) component parts and also requiring different methods of preparation for said component parts (drawing for the coupling tube 10, pressing for the coupling arms 11 and forging for the clamp member 12) with a large number of working steps, whereby the manufacturing cost is inevitably increased.